Field
The present disclosure relates generally to wireless communication, and more particularly, to signal modulation.
Background
Orthogonal frequency-division multiplexing (OFDM) is a popular signal modulation scheme having various advantages. One such advantage is that OFDM readily supports flexible multiple-user access. OFDM and orthogonal frequency-division multiple access (OFDMA) are widely used in modern wireless communication systems such as Wireless Local Area Networking (WLAN), Long-Term Evolution (LTE), etc.
OFDM signals may have a relatively high peak-to-average power ratio (PAPR). High PAPR may lead to the necessity of high-resolution analog-to-digital converters (ADCs), high-resolution digital-to-analog converters (DACs), and power amplifiers having high linearity. Oftentimes, high-linearity power amplifiers have lower power efficiency, due to the amount of power needed to produce an effective signal, as well as higher cost. Although OFDM may be commonly used in downlink transmissions from a base station, such as an evolved Node B (eNB), the disadvantages of power and cost associated with OFDM can make OFDM poorly suited for mobile devices requiring reduced power consumption to maintain long battery life.
For reduced PAPR, single-carrier frequency-division multiple access (SC-FDMA) can be used. The reduced PAPR associated with SC-FDMA enables increased power efficiency when compared to OFDMA, making SC-FDMA suitable for transmissions from a mobile device/user equipment (UE), such as an uplink transmission of a UE operating according to the LTE standard of telecommunication. However, although SC-FDMA reduces PAPR when compared to conventional OFDMA, SC-FDMA still has a relatively large PAPR when a relatively large number of tones are allocated for the uplink transmission of the signal.
Much effort has been made to reduce signal PAPR of OFDM and SC-FDMA signals without significant success. Various schemes have been proposed that often entail complicated signal processing, loss in bandwidth efficiency, and/or increased inter-carrier interference. One example is the attempt to apply constant-envelope modulations, such as minimum-shift keying (MSK) and Gaussian MSK (GMSK), to SC-FDMA. Due to their nonlinearity, implementation of MSK and GMSK in SC-FDMA is not straightforward, and entails significant bandwidth expansion and loss in error performance. With the advent of internet of things (IOT), there is a growing need for very low-power wireless communication devices to enable extended battery life. This in turn calls for modulation schemes with very low PAPR.